Note: Descriptions are shown in the official language in which they were submitted.
WO 93/16449 PCI'/US93/01010
CA21 1 7474
DUAL CXANN~L ~LASg BREA~
t~r~ Or ~ r---~t ~nv-n~rn
Th- rollow1ng l~ lon r-l-t-- to a gla~-
br-ak ~t~t_~ and ~or- partlcul-rly to an rcou~tlc
~tonslng da~tc- that s-n--- two dlrr-r-nt r,. _~r, c~ar-
actoslctlc~ or br~~t~1n~ gla-- ~nd provld - an ~lar~ upon
tn- dot-ctlon Or both c~ wlthln p,~ tls~
rr~"t-- Th- lnvontlon r--ult- rron th- ~ that
~r~-t~1nq gl~-- p.Jd - - hlqhly c - ~ l-tlc p~ or
acou~tlc wav -, rnd ln psrtlcu~ar, p.Jd~ -- a ch-rao-
t-rl-tic poeltlv- low r.., - I acou-tLc wavo and a h~tg~
r._ - I ~-t Or acou-ttc wav - that rollow th- inltlal
low ~r~ P~~'
In tn~ p--e, qla-- br-ak 1~ hav-
at~ to ~l~lnat- th- G~ -- 0~ ral~t- alarr-
~y ~ocu-ing on hlgh and low ~.-, I charact-r:~tlc-
or br-ak~ng qla-- Th- U-S- pat-nt to Yanagl, No
4,091,660, d-t-ct- ~lgnal- ln a ~ rrng- o~
th~n 50,000 cyclo- and or gr--t-r than l00,000 cycl--,
produclng an _ hl~nq ~Lgnal ~or an al~rn wh-n both
rL~L-- I - . ~ ar- pr --nt at eh- ~a~ tiat- Oth-r
d-vic-- , 1~- that dlr~-r nt ~ ,~~~ t ~tay
b- pr---nt ~t dL~-r nt tl2-- ~n n ~ ~t al U 8
2S Pat-nt No 4,668,9~, it ~ th-t br~aklnq gl---
z~ an ~nltlal low r.. , I thunp : t l. - l ~round
350 ~z ~t ~ by ~ hLgh ~ C~ L~ t
around 6 s kHz Ih- 6 S kHz ~lgnal 1- lndlcatlv- or
glae- that br-ak- a- lt rall- on th- rloor and ~
produclng ~ t~ inq ~ound But a- polnt-d out ln Ab-l
ot al U s P~t-nt No. 4,83~,558, on- can not alway-
pr-su~- that gla-- onc- brok n wlll produc- th- t~n~1~nq
~ound, partlcularly lr th- gla-- p n- or wlndow l-
sleuatad abov- ~ carp-t ln an o~lc- or r-~
For zou- tl~- lntru-lon ~ _ hav- ~a~- u~-
Or th- p' that th- op-nln~ or a door or ~lndow
p.~ - - an ~n~ra~~~1c ~._ ~ wav- that ~tay b- ~ t~ ~ I
Sul3smuTE SHEET
WO93/1~9 PCT/US93/01010
CA21 17474
by a sensitive microphone or other acoustic transducer
having a frequency response in the region of one to five
or ten cycles per second. An example of such a device is
shown in Yarbrough et al. U.S. Patent No. 4,8S3,677. The
Yarbrough device also includes a glass break detector
circuit that is coupled to the same microphone. Either a
high frequency or a low frequency event will trigger an
alarm if either p.~d~ces the ~p~-u~Liate frequency
~e~L.u~. Furth~ c, it has been reoogn;~od that the
opening of a door or window pLvduces negative-going air
p~S~ULe in the first instance and acoustic detectors
which are intrusion detectors have been ~ocignod to take
adv~..Lage of this fact. An example is shown in Goldstein
et al. U.S. Patent No. 4,991,145.
The afo~ Lioned glass breakage and intrusion
de~ecLo~ take adv~l,La~c of some of the characteristics
of breaking glass but do not always inhibit false alarms
which may be p.~duced by events that have frequency char-
acteristics similar to those pL~duced by breaking glass.
II~ CL they fail to take into account the fact that,
ospecj~lly in the low LLe~uc..~y region, different types
of glass emit different LLc~uenoy spectra when they
break.
Summarv of the Present Invention
The present invention takes advantage of the
fact that breaking glass of every known type may be
characterized by a positive low frequency acoustic wave
~L~duced by an inward flex of the glass as it is being
broken from the outside of the room or enclosure to be
monitored. This low frequency flex is followed by high
frequency acoustic waves having a characteristic
frequency spectrum.
According to the invention, an intrusion
detector for detecting the breaking of a window, glass
pane or the like includes an acoustic transducer such as
a mi~Lu~h~--e and a signal processing circuit responsive
W093/1~9 PCT/US93/OtO10
CA21 1 7~74 3
to the acoustic trAncdll~or for detecting a first low
frequency positive acoustic wave generated by an inward
flex of the glass and an alarm responsive to the signal
processing circuit. The system further includes a high
frequency bAn~rAec filter for detecting high frequency
acoustic waves characteristic of breaking glass and a
co;nri~on~e logic circuit that enables the alarm when the
low f~e~uè1.~y acoustic wave is detected during a prede-
to-n;nod time window that begins with a high L~yu~n~y
event generated by the breaking glass. The alarm may
then be triggered by s l;ng the high frequency output
of the trAne~ or at a time after the initial time
window. The logic of this system takes zdv~"~age of the
fact that the requisite high fle~Uen~ ~e~,u~ of
acoustic waves will follow the initial positive low
f~e~u~ y wave p.~duced by the inward flex of the glass
pane or window.
A circuit may also be provided to inhibit the
alarm upon the detection of negative-going low frequency
rher followed by high frequency sounds that would
otherwise partially enable the alarm. The alarm inhibit
feature significantly reduces the ;n~idon~e of false
alarms such as those that would be caused by a legitimate
opening of a door or window followed by high frequency
sounds such as the jangling of keys. The invention also
takes advantage of the fact that, regardless of the type
of glass, the low frequency c -nt of breaking glass
lies in the frequency region between 50 Hz and lOO ~z and
that the breaking of glass is always initiated by a posi-
tive compression wave. Infrasonic detectors of the priorart frequently operated on the principle that a glass
break creates a low frequency sound that resonates the
room, coupling it to the outside world through the broken
window. The problem, however, is that such low frequency
resonance may also occur for a large number of events not
associated with breaking glass.
WO93/1~9 PCT/US93/01010
~A211 7474 4
It is a principal object of this invention to
provide a glass break detector that accurately discrim-
inates between the sounds of breaking glass and other
sounds so as to prevent false alarms.
A further object of this invention is to
provide a glass break detector which can detect the
breaking of different types of glass.
Yet a further object of this invention is to
provide a method for detecting the breaking of a glass
panel on the perimeter of an enclosure such as a room by
detecting a positive low freauency plesau.a wave followed
by a high L~eyuel-uy sound having a L ~yu~nuy .~e~L.
which is characteristic of breaking glass.
The foregoing and other objectives, features,
and adv~rLa~s of the invention will be more readily
understood upon consideration of the following detailed
description of the invention, taken in cunju-,uLion with
the A~' , ying drawings.
Brief DescriPtion of the Drawinas
FIG. l is a block schematic diagram of the dual
channel glass break detector system comprising the
invention.
FIG. 2A, 2B and 2C is a detailed schematic
diagram based upon the block schematic diagram of FIG. l.
FIG. 3 is a waveform diagram illustrating the
essential system timing.
Detailed DescriPtion of the Invention
Referring to FIG. l a glass break detector
includes a microphone Xl coupled to a low freauency band
pass filter lO and a high freauency filter 40 in parallel
with a resistor Rl7 which is coupled to a source of
supply voltage Vdd. The low freauency band pass filter
lO is coupled to a set of threshold comparators 20 which
define different set points for low freauency . ~~ts
of the signal from the microphone Xl. The output of the
WO93/1~49 PCT/US93/01010
CA21 17474 5
threshold comparators 20 is coupled to a flex logic
circuit 30. The high frequency filter 40 is coupled to
trigger comparators 50, which initiate the timing logic
for the system and are coupled to timing logic circuits
60. The output of the timing logic circuits is coupled
to the flex logic circuit 30 and to a NAND gate G23. The
output of the high frequency filter is also coupled to a
f.eyuè1..y to-voltage converter 70 whose output is in turn
coupled to a window comparator 80. The output of the
window ~ ~LUL 80 drives a timed latch 90. Both the
timed latch 90 and the frequency-to-voltage converter 70
receive timing inputs from the timing logic circuit 60,
and the outputs of the flex logic circuit 30 and the
timed latch 90 are also inputs to NAND gate G23. The
output of NAND gate G23 is connected to an alarm logic
circuit lO0. The details of the alarm logic circuit lO0
are not shown but the circuit is active when the output
of NAND gate G23 is low. This will occur only when all
three inputs to NAND gate G23 are high, and the alarm
logic circuit lO0 then develops audible and/or visual
alarms. The details of such circuits are well known to
those of ordinary skill in the art.
Referring to FIG. 2A the microphone Xl is an
electret microphone having a frequency response from
20 Hz to 20 kHz plus or minus 3 db whose output polarity
is positive for an increase in al ~ ric ~Le~u~e and
negative for a decrease in atmospheric pressure. The
microphone should be of the type that has a wide dynamic
range, greater than 120 db, and an omni-directional
pickup pattern. The bias current for the microphone is
supplied from a 5 volt DC source through resistor Rl7.
The output of the microphone is coupled to a
high frequency channel comprising high frequency filter
40. Although the microphone chosen for this application
has a wide frequency response and active filtering is
used throughout, it should be recognized that frequency
shaping could be accomplished partially or even entirely
WO93/1~9 PCT/US93/01010
CA2i 17474 6
in the mi~-opl-~-.e design rather than in the filter
design. In order to detect the breaking of laminated
window glass when the microphone is at a distance from
the window, the high L.ey~n~ filter 40 must have a
minimum slope of 6 db per octave from o Hz to 5 kHz and
then rise to a 12 db per octave slope by 8 kHz. Above
20 kHz the filter response is rolled off at a minimum -
6 db per octave rate to attenuate undesired ultrasonic
signals.
The network including capacitor Cl resistor Rl,
capacitor C2 resistor R2, and ~ lifl~r Al form an active
band pass filter with gain. Capacitor Cl isolates the DC
signal of the mi~ u~h~,,e from the circuitry of the filter
and in ~--ju~-~Lion with resistor Rl ~tDrmin~e a high
pass pole near 19 kHz. This : ' ci 7~e high L.~ Pe
at a rate of plus 6 db per octave within the band width
between 0 Hz and 19 kHz. Capacitor C2 in conjunction
with resistor R2 det~rm;n~e a low pass pole near 24 kHz
which provides a -6 db roll off per octave of ultrasonic
L.-y~ ;ec. The network comprising capacitors C3, C4,
C5 and resistors R3, R4, and R5 and amplifier A2 form a
low pass filter with peaking. Capacitor C3 isolates the
DC offset of the first stage from the second and in
~..ju-.~Lion with resistor R3 det~-min~c a sufficiently
low high pass pole near 16 Hz. The network in the feed-
back path from amplifier A2 peaks the .~..se at 20 kHz
and provides additional rise in the slope from +6 db per
octave. Amplifier A3 forms an additional amplification
stage with the ratio of resistor R7 to resistor R6
setting the gain and capacitor C6 isolating the DC offset
of amplifier A2 from the circuitry of amplifier A3.
Capacitor C6 and resistor R6 determine a sufficiently low
high pass pole near 160 Hz.
The freyuency to voltage converter includes an
amplifier A6 that converts the output of the high
frequency filter 40 from the amplitude domain to the
frequency domain. The output of A6 is gated by an AND
W093/1~9 PCT/US93/OtO10
CA211 7474 7
gate Gl that is triggered by the NG (noise gate) timing
signal. A signal above the zero voltage threshold on the
comparator amplifier A6 turns off switch MPl and turns on
switch MNl placing an amount of charge on capacitor C7
that is detDr~in~d by capacitor C15 and resistors R8 and
R9 as well as the bias voltage across capacitor C7. When
the signal drops below the threshold of the comparator,
switch MNl is turned off and switch MPl is turned on,
zeroing capacitor Cl5 and allowing the charge on capac-
itor C7 to leak to ground through resistor R10. Thevoltage developed across capacitor C7 in response to this
periodic signal subtracts against the voltage to charge
capacitor C15 and reduces the amount of charge de}ivered
to capacitor C7. The output of the frequency to voltage
converter is prebiased so that it lies between the two
trigger points of the window comparator 80. This is done
by turning on switch MP2 and connecting a voltage source
VDD to the voltage divider which is formed by resistors
Rll and R10 which then charges capacitor C7.
The output of the L-~yuen~y to voltage
converter is connected to the window comparator 80 which
includes comparator amplifiers A7 and A8 which have out-
puts coupled to AND gate G2. The output of the frequency
to voltage converter 70 is prebiased through switch MP2
to keep its output between the trigger points of +800
millivolts and +340 millivolts which are inputs to
comparator amplifiers A7 and A8 respectively. Voltages
that result from frequencies that lie within the band of
interest will allow the output of the frequency to volt-
age converter 70 to stay between these trigger points.Many false alarms have average frequencies that are
always below the threshold of the window comparator 80,
and some false alarms start out initially below the
threshold and then go above the threshold into the
window. Prebiasing the output in the window makes these
events invalidate the signal by driving it out of the
window. This is due to the fact that all true glass
WO93/1~U9 PCT/US93/01010
CA21 1 7474
breaks have average frequencies that will lie in the
window except for some worse case tempered glass breaks
which are initially below the bottom of the window but
then climb into the window within the first 10
millicocnn~c.
The output of the window comparator 80 sets a
timed latch 90 that in~ oc NAND gates G4 and G5. The
input to the NAND gate G4 is an OR gate G3, and the other
input to the OR gate G3 is a timed 10 mi 11 i cPC~n~ pulse.
This pulse occurs when the system is initially triggered
as will be oYr' A; nod below. The 10 m; 11 i cec~n~ pulse
keeps the timed latch 90 from resetting during the first
10 mi 11 i ce~An~c of an event which may be a valid glass
break. This is because as oYrl A i nod above, some types of
lS glass, particularly t~ ~=d glass, can break without
nPcoccArily generating L.~luo~ iec during the first 10
mi 11 i coc~c which would be within the limits of the
window comparator 80. The 10 mi 11 i ceC~n~ pulse keeps the
latch 90 from resetting if the break is of this type of
glass. After the initial 10 milliseconds, the output of
the window comparator 80 alone will determine whether the
latch 90 is reset. The latch is enabled by the timed NG
(noise gate) signal whose origin will be oYp1Ainod below.
The output of the microphone Xl is also
connected to a low Lle~u~ y band pass filter 10 which
consists of two amplifiers A9 and A10 together with
iate feedback networks. This filter has a
frequency response that : 'Aci 7es the 50 Hz to 100 Hz
region, since it has been empirically determined that the
initial flex made by glass just prior to its being broken
is found within this frequency region. Also the positive
pressure wave resulting from the initial inward flex just
prior to a break is of higher magnitude than an outward
flex oCroc;Ally for tempered glass. When tempered glass
breaks, the outward flex after the initial inward flex is
highly damped, thus detection schemes that are triggered
by either an outward flex or by cycle counting may fail
WO93/1~9 PCT/US93/01010
CA21 17474
to detect many such breaks. The filter lO is therefore
configured to have an output in the low frequency region
that naturally occurs in all types of glass breaks.
The output of the filter lO is connected to a
threshold comparator network 20 which includes compar-
ators All, Al2 and Al3. The comparator amplifier All
detects p~S~ULa waves associated with objects breaking
a window and its threshold is set s~ f f i'-- j ~ntly low to
detect worst case flexes. This is because it has been
d-term;ne~ that tempered glass, _Cp~ci~11y, generates a
positive ~-as~u.a wave that is much lower in amplitude
than those caused by breaking plate and laminated glass.
C ator Al3 detects high level p~as~u.e waves created
in very small rooms or airlocks which would be detected
before a window or pane actually breaks. C - ~tor
amplifier Al2 is part of an inhibit network that detects
negative ~.~s~u.a which is not associated with glass
breaking. The outputs of these three comparators are
analyzed in the flex logic circuit 30.
Even though the window flexes before it breaks,
the high fre~-n~ q of the break will reach their peak
before the low frequency pressure wave resulting from a
valid flex does and are thus easier to detect first. It
has been empirically det-rm;~ d that a valid flex is
always detectable within less than lO m; 11; ~e~ nAc after
detection of the first high C-a~uen~y ~ -nts of the
break. Therefore, a positive transition above the thres-
hold of comparator amplifier All triggers a l millisecond
one shot comprised of amplifier G22 and flip flops F27
and F28, the purpose of which is to indicate an immedi-
ately occurring increase in positive al ~t.eric pres-
sure. Either the output of comparator Al3 or All will
set the latch comprised of NAND gates G20 and G21 unless
inhibited by the latch comprised of NAND gates Gl4 and
Gl5. Because of the lO millisecond input to NAND gate
Gl9, this event must occur, if at all, within the first
lO milliseconds of the break event. The output latch,
WO 93/16449 PCI/US93/01010
CA21 17474 lo
which is comprised of NAND gates G20 and G21 is enabled
by the NG signal.
In the case of an initially negative-going
pressure wave occurring within the first 10 mill;~ecnn~c,
latch G14, G15 will be low preventing AND gates G16 or
G17 from passing a valid high signal to OR gate G18.
This forces the latch G20, G21 low which in turn forces
the output of NAND gate G23 high, disabling the alarm.
The timing logic network 60 is triggered by a
high eyuel~uy event initiated by the trigger comparator
circuit 50. This circuit includes two trigger l;fi~s
A4 and A5. Comparator amplifier A5, which has a rela-
tively low threshold, institutes a five m; 11; ~cn~
retriggerable one shot whose output resets flip flop F4.
If the amplitude of the high frequency event is high
enough, comparator amplifier A4 is triggered which clocks
flip flop F4 and p~uduces the NG (noise gate) pulse.
From the noise gate pulse a chain of flip flops F5-Fll
are triggered which develop pulses at various times and
having various duty cycles. A 10 m; 11; ~cnn~ timing
pulse whose leading edge is substantially aligned with
the NG pulse is p,uduced by flip flop F12. This pulse is
then provided as an input to NAND gates G15, Gl9 and OR
gate G3. The AND gate G10 produces a 77 millisecond
pulse (i.e., its leading edge is initiated at 77 milli-
seconds) in order to enable NAND gate G23. Thus, accord-
ing to the system logic, if the high frequency ,_ ~nts
of the break have not driven the output of the frequency
to voltage converter 70 out of the window est~hl;~h~d by
the window comparator 80 after the initial 10 milli-
seconds of the break, and before 77 ms after the break,
and if the initial low frequency pressure wave OceuLL~d
within the first 10 milliseconds of the break, a valid
alarm condition will be sensed.
FIG. 3 illustrates the essential timing of the
system. A typical glass break signal generates the
filter outputs shown in FIG. 3 and the NG and 10
WO93/1~9 PCT/US93/01010
'C~2~ ~ 7~
millisecond pulse signals are generated accordingly.Because the break event is in the correct frequency range
and of sufficient amplitude to trigger the timing logic
in network 60, the output of the low frequency band pass
S filter lO goes sufficiently high within the first lO
millie~cnn~c to set the latch G20, G21 at the output of
the low frequency channel. The time between the end of
the lO millieecnnA pulse and the beginning of the pulse
at 77 milliseconds is a period during which the high
o r e~uel~y channel can be driven out of the window estab-
lished in the window comparator 80 by an invalid signal.
If it is not driven out of the window, however, at the
initiation of the pulse at 77 millicecnn~e, the alarm
will be triggered. The noise gate signal can be reset
anytime the high Lle4ueney signal goes below its
threshold for greater than 5 millieecnn~e.
It should be appreciated that various clock
rle~ue..ey signals and voltages are used herein but the
circuits generating them are not shown. For example, the
signal MR~ is a master reset pulse generated upon power-
up of the system by the power supply. These signals are
produced by conventional oscillators and voltage supplies
and as such their details are well known to those of
ordinary skill in the art.
Various modifications to the above invention
are possible without departing from the spirit of the
invention. For example, the high and low rle~uè..ey
filters may be of different configuration from those
shown and could even be incorporated in the trAne~n~r
design. Also, the frequency to voltage converter andwindow comparator circuits have been shown with the
system biased to assume a valid signal which can be
forced out of the window. This gives the system a faster
response and makes it easier to detect the breaking of
tempered glass. The system could be configured, however,
so that a valid signal must occur before an enabling
signal would be provided by a latch or the like.
WO93/1~9 PCT/US93/01010
~A2 1 1 7 474 12
The terms and expressions which have been
employed in the foregoing specification are used therein
as terms of description and not of limitation, and there
is no intention, in the use of such terms and expres-
sions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that
the scope of the invention is defined and limited only by
the claims which follow.
